One of the potential issues inherent in our approach is when each video is first uploaded and becomes available on the system without any prior playback usage data. The “cold-start" issue is typical of many usage-based machine learning algorithms such as recommender systems ([1]} [2]}) where the effectiveness of the approach relies on its usage over time. In our system, when a video first becomes available, the visualisation does not have usage data from which to calculate and populate the timeline. As soon as a student starts using a video, its usage will be captured and reflected as a low, yellow area at the bottom of the timeline. A manual indication of the important parts by the lecturer at the time of uploading each video may be a simple solution that could also serve as a way to lead a more desirable evolution of the contour. However given one of the strengths of our approach is fully-automated shaping of the visualisation without extra efforts by a human, other more automated ways to draw the data will be an important topic of further study. For example, some studies used supervised machine learning techniques applied to lecture video images to determine the important parts in videos [3]} or applied to the usage data (selecting a video, seeking within the video, as well as the heartbeat rates of the students) to develop a computational model of the usage patterns of students to predict a more desirable pattern [4]}. Taking a bottom-up indexing approach (i.e. important parts emerge by looking at the video/usage data) rather than top-down (i.e. system first defines and codes in what the important events are), bringing some of these computational approaches into our system may help tackle this issue in a way aligned to what we eventually envision. In our second deployment, the same videos used in the first deployment were uploaded afresh without any use of the data captured from the first deployment. One possible approach would be to plug in the usage data from a previous running of the course (if it has run in previous year(s)) at the start of the course, to be slowly overridden by the actual usage once this was sufficient.
